1. Field of the Invention
This disclosure relates to a liquid crystal display device and more particularly to a liquid crystal display device adapted to minimize noise which is caused by vibrations from electric currents flowing through lamps.
2. Discussion of the Related Art
As the information age progresses, display devices visually displaying a large amount of data on the basis of an electric signal are being rapidly developed. As a result, flat panel display devices with superior features such as light weight, slimness, and low electric power consumption have been widely distributed. Flat panel display devices include liquid crystal display (LCD) devices, plasma display panel (PDP) devices, field emission display (FED) devices, electro luminescence display (ELD) devices, and so on. These cathode ray tubes of related art are rapidly being replaced with flat display devices
In order to form an image (or picture), LCD devices receive the light necessary to form an image (or picture) because they cannot emit their own light. In other words, LCD devices are light receiving type devices. Accordingly, LCD devices have to include a separate light source, for example, a backlight unit. The backlight unit used in LCD devices is classified as a direct type or an edge type according to the placement of (a) fluorescent lamp(s). A direct type backlight unit includes a plurality of fluorescent lamps arranged on a plane under a liquid crystal panel, while an edge type backlight unit includes a fluorescent lamp disposed on one side portion of the light guide plate.
More specifically, an edge type backlight unit includes a light guide plate guiding light as well as a lamp portion disposed on one side surface of the light guide plate. The lamp portion includes a light emitting lamp, lamp holders installed to receive and protect both ends of the lamp, and a reflective plate encompassing the outer circumference surface of the lamp. One side surface of the reflective plate is inserted into one side surface of the light guide plate. The reflective plate reflects light emitted from the lamp toward the light guide plate. Such an edge type backlight unit is mainly used in LCD devices of relatively small sizes which are applied to the monitors of laptop and desktop computers. The edge type backlight unit has a uniform light distribution and a long life span of internal parts, and allows the LCD device to be thinner.
The development of direct type backlight units began with the enlargement of LCD devices. The direct type backlight unit includes a plurality of lamps arranged under a diffusion plate in order to directly irradiate light on the entire surface of a liquid crystal panel. As such, the direct type backlight unit has a higher light efficiency than that of the edge type backlight unit. In view of this point, the direct type backlight unit is mainly used in large-sized LCD devices requiring a high level of brightness. Meanwhile, the direct type backlight unit includes many lamps. A large-sized monitor or television including an LCD device with a direct type backlight unit has a longer life span than a laptop computer. Due to these reasons, a direct type backlight unit may be more often out of order than an edge type backlight unit, and there is a high possibility that part of the lamps will not function due to the end of their life span.
Actually, a direct type backlight unit applied to an LCD device includes a plurality of fluorescent lamps arranged in an inner space (or cavity) formed by upper and lower frames, a reflective plate disposed under the plurality of fluorescent lamps and configured to reflect light, and optical sheets disposed over the plurality of fluorescent lamps and configured to diffuse and converge light from the plurality of fluorescent lamps. The plurality of fluorescent lamps is inserted into fixing members on a balancely printed circuit board (B-PCB) and is placed into a bottom cover. The B-PCB and the bottom cover are insulated from each other by an insulation layer formed between them.
When the plurality of fluorescent lamps generate light using electric currents each corresponding to lamp drive voltages, vibrations are caused by the electric currents flowing through the fluorescent lamps. The vibrations are transferred to the B-PCB. The transferred vibrations reach the bottom cover in such a manner that they are reduced to a very slight degree by the insulation layer.
However, the insulation layer decreases in thickness as the LCD device is gradually made thinner. As such, the distance between the B-PCB and the bottom cover is reduced. In addition, the distance between the plurality of fluorescent lamps and the B-PCB is reduced. Due to these reasons, the vibrations caused by the electric currents flowing through the plurality of fluorescent lamps largely increase in comparison with those of the related art. Accordingly, noise may be generated on the entire surface of the bottom cover.